A pipeline typically has an outer coating to protect the pipeline from corrosion and other detrimental effects, particularly when the pipeline is buried underground. This coating degrades with time, and, if the pipeline itself is to be prevented from sustaining further permanent damage, the pipeline must be dug up, the old coating removed, the surface of the pipe conditioned and a new coat of protective material applied to the pipeline.
When initially building a pipeline, the individual pipe sections are typically coated prior to shipment to the final location, where they are welded together to form the pipeline. By coating the pipe sections prior to shipment, it is possible that the coating will be damaged in shipment. Also, the welding of the pipe sections together destroys the coating at the welded ends. Coating damage due to shipment and welding must be repaired on a spot basis as the pipeline is constructed. Because of the excellent corrosion protection, impact and adhesive properties, it would be advantageous to coat the entire pipeline with a plural component polyurethane material at the construction site. However, no technique has been developed to date to do so economically and at the production rates required.
In a typical pipeline rehabilitation operation, the pipeline will be uncovered, and a lifting mechanism, such as a crane, will be used to lift the exposed portion of the pipeline out of the ditch and rest the exposed pipeline on skids to provide access to the entire outer surface of the pipeline in the portion between the skids. The pipe must then be cleaned, the outer surface of the pipeline prepared to receive a new protective coat, and the pipeline then recoated.
Initially, manual labor was required to remove the old coating with hand tools such as scrapers. This technique is obviously time consuming and quite expensive. Various attempts have been made to provide more automation to the cleaning procedure, including U.S. Pat. No. 4,552,594 issued Nov. 12, 1985 to Van Voskuilen and U.S. Pat. No. 4,677,998 issued Jul. 7, 1987 to the same inventor. These patents disclose the use of high pressure water jets which are moved in a zigzag path along the pipe surface to be cleaned to slough off the coating. While devices of this type have been an improvement over manual cleaning, there still exists a need in the industry for enhanced performance in the cleaning and recoating operation.